Two-way radio signaling system



June 21, 1932. SM1-[H TWO-WAY RADIO SIGNALING SYSTEM Filed July 26, 1928 2 Sheets-Sheet l narran: i fin #9e/vial Feczrzng denial.

L- gwwmtoz uns aci ver June 2l, 1932. SMITH TWO-WAY RADIO SIGNALING SYSTEM Filed July 26, 1928 2 Sheets-Sheet 2 Patented June 21., 1932 UNITED STATES PATENT OFFICE-7 LARRY L. SMITH, OF IVIONTICELLO, KENTUCKY, ASSIGNOR OF ONE-FOURTH TO JAMES N. COX, OF COOKEVILLE, TENNESSEE, ONE-FOURTH T'O CHARLES H. "MOORE, OF GLASGOW, KENTUCKY, AND ONE-TENTH T0 EDWARD' C. WARNER, OF COOKEVILLE,

TENNESSEE '.lW'O-VVAY' RADIO SIGNALING SYSTEM Application led J'uly 26, 1928. Serial No. 295,541.

rihis invention relates to a two-way radio signaling system comprising'a radio set incorporating interconnected or intercoupled transmitting and receiving circuits arranged for simultaneous transmission and reception of signals for two-way communication.

The primary object of this invention is to provide an improved, simplified and practical system for two-way radio communication in which complicated circuits requiring fine adjustments which are not practical for commercial equipment have been avoided.

In` the two-way signaling system according to the present invention transmitting and receiving circuits have been combined to serve the dual functions in which the frequencies for transmitting and receiving differ suiiiciently so as not to interfere with each other. In a practical form of the system the receiving circuits include a receiving antenna7 detector and oscillating circuits together with suitable output amplifying circuits; the transmitting circuits include la superimposed modulating circuit which cooperates with the oscillator circuit which is common to both the transmission and reception of signals and aseparate transmitting antenna, and a filter is connected between the receiving and transmitting circuits for preventing interference between these circuits during the simultaneous transmission and reception of signals.

The hcterodyne principle of receivingv is employed in which the intermediate frequency between the frequencies of the detector and oscillator circuits is passed through the intermediate frequency amplifier or filter circuit and detected in the usual way, and when acting as a transmitter the oscillator `circuit is modulated by a voice frequency impressed upon it by a transmitting modulating circuit for transmitting at a different frequency from that of the incoming signals. In this way, the oscillator has a dual function acting both for input and output for simultaneously receiving and transmitting without interference.

Further objects and details of the invention will appear as described in connection with the accompanying drawings and hereinafter set forth and claimed.

The drawings illustrate preferred embodiments of the invention which have proven highly eiiicient and economical in operation, in which v Figure l "diagrammatically illustrates the principles of transmission and reception between two stations employing systems of twoway radio signaling in accordance with the present invention; v 'Y Figure 2 and Figure 2A, when combined represent a circuit diagram ofaradio set incorporating the two-way signaling system;

Figures 8 'and 4 are circuit diagrams of modified forms of the two-way signaling systems in accordance with this invention. i

Referring to Figures 2 and 2A, the circuit diagram illustrated incorporates the circuits of a super-heterodyne receiver and 'transmitter circuits comprisinga modulating circuit and an oscillator circuit common to both the receiver and transmitter circuits.

The circuits functioning for receiving include the detector and receiving antenna circuits D,- oscillator circuits O, intermediate frequency amplifier circuits A1", second detector circuits D2, audio frequency amplifier c ircuits Aa and 'receiver circuit R. The circuits functioning for transmitting include the transmitting modulating circuit M, the common oscillatorcircuits O which are common for both transmitting and receiving and transmitting antenna circuit TA. y

.The receiving Aantenna-circuit of the dei 85 tector circuit preferably. includes an aerial l, untuned primary inductance L1 of a coil 2- and ground connection 3. Coil 2 has a secondary inductance L2connectedwith a variable condenser C1v for tuning the circuit to the wave length Vofthe incoming signal, and this circuit is connected with thedetector tube VTl, comprising the grid circuit of this detector tube, The plate circuit ofthe detector tube includes a regeneration or .ticklerinductance. coil L3 which is inductively coupled with the coil 2. This plate circuit feeds througha receiver pick up inductance coil L9, inductively coupled with the oscillator circuits O to the primary of the first une transformer T1 of the intermediate frequency amplifier circuits.

The oscillator circuits O include an oscillator tube VT2, the grid circuit of Which includes a grid oscillator inductance coil L5, a radio frequency choke coil L4 and a variable grid resistance VRl, and the plate circuit includes a plate oscillator inductance coil L7. Y

Inductance coils L5 and L7 are inductively coupled and capacitively connected by means of a small by-pass condenser C5 (about .0005 m. f.), for receiving incoming signals. These Oscillator inductances are tuned by means of a variable condenser C2. These inductances areinductively coupled With the inductance coil L9, referred to above as being connected in the plate circuit of the .detector tube VTl and the first transformer T1 of the intermediate frequency amplifiers, whereby the frequency of the oscillator circuit is impressed upon that of the detector circuits for producing a certain heterodyne frequency hereinafter described in detail to which the intermediate frequency amplifiers Will respond.

The intermediate frequency amplifying circuits comprise a number of stages each having an amplifying tube VT4 and ampli'- fyingtransformers T1 and T2. The transformer T1 Which feeds into thefirst amplifying tube has a tuned primary Winding Which responds to said heterodyned frequency referred to above. The primary Winding 4 of this transformer 'is connected With a condenser C6 Which may besemi-variable or adjustable for adjusting the Wave length of this'circuit to the .desired frequency found to be most efiicient for the intermediate or heterodyned frequency amplifier circuits in the two-Way signaling systems and also functioning as a filter or by-pass to prevent interference between the transmitting'and receiving circuits as Will be hereinafter 'described. The secondary Winding of this transformer is connected With the grid of the first amplifying tube and the plate of this tube and each tube of the succeeding stages feeds into the primaries of the transformers T2 and, similarly, the secondaries of the transformers T2 feed into the grid of the .neXt tube. The returns of the secondary windings of transformers T1 and T2 are connected with a potentiometer 5 across the filament or Afbattery and With the common negative ofthe A and B batteries, or other sources of current througha by-pass condenser C7 in the vvell known manner.

The secondary Winding of the last transformer T2 feeds into the grid of detector tube VT5 of the second detector circuits D2, this grid circuit including thegridleak resistance R2 and grid condenser C9. A by pass condenser C8 may be connected across the plate circuit of this detector tube VT5, which circuit feeds into the audio frequencyamplifying circuits Aa in the usual manner. The audio frequency amplifier circuits, as shown7 include two audio transformers AT-l and tvvo audio amplifying tubes VTG Which are in turn connected With the receiver R. The various circuits are supplied With current at the desired potentials in the usual manner and the various tubes may be controlled by means of rheostats or filament ballast resistance R3. A negative grid potential provided by a battery C-B2 may be employed in the circuits of the audio amplifier tubes to advantage.

` The circuits above described comprise the receiving circuits of the super-heterodyne receiver of the tvvovvay signaling system and in operation its tuning is controlled by means of the tvvo variable condensers C1 and C2, condenser C1 being adjusted for tuning the detector circuits D to the Wave length of the incoming signal and condenser C2 being adjusted to tune the oscillator circuits O to a frequency to produce with the frequency of the detector circuits a heterodyne frequency to Which the tuned intermediate frequency amplifier circuits A1' have been adjusted to respond. The signals are then passed through the second detector circuits D2 and audio frequency amplifier circuits Aa and receivercircuit R.

In the transmitting circuits, thetransmitting modulating circuits M include a microphone MK 'and modulating transformer Mod-T connected in the grid circuit of the transmitting modulating tube VTS to Which a negative grid bias potential may be supplied by a battery O Bl.

The plateV circuit of this modulating tube is connected through a radio frequency choke coil L8 with the plate coil L7 of the oscillator inductances. The B battery current for both the oscillator tube VT2 (which serves the dual function in the two-Way signaling system) and the transmitting modulating tube VTS is supplied to these tubes through an audio frequency choke coil Hl-l directly to the plate of tube VT3 and through the radio frequency choke coil L8 and plate oscillator coil L7 to the plate of tube VT2. A milliammeter mm may be connected in this circuit to indicate the power supplied to these tubes Which may be reUulated according to distances and transmitting conditions. The audio frequency choke coil Hl-l is eective in Amaintaining` a constant supply of power to the tWo tubes during the modulation of the power delivered through the oscillator tube when an audio frequency is impressed on the grid of the modulator tube VT3. The radio frequency choke coil L8 is effective to prevent the radio frequency currents in the oscillator circuit from passing and thereby prevents interference With the functioning of the oscillator.

The oscillator circuits have been described connection. with. the receiving circuits and theinter-connection of the transmitting modula-tor .circuits and the oscillator circuits O have been set forth. above aswell: as the manner* in which the power in the tuned oscillator circuiti is; modulated by-means of thel audio frequency modulator tube VT3. The tuning of the" oscillator has also been described in connection with the receiving circuits as being accomplished with the variable condenser Although notY always necessary, the plate-:circuit may also be tuned with a variable condenserC3. However, as. hereinafter: set forth, tuning of the oscillator'may berv best accomplished by omitting the plate condenser C3 and bridging the grid coil L5 with the condenser C2.

TheV transmitting antenna circuit Ta includes an aerial 6 connected at one end of the antenna inductance or transmitter aerial pick-up coil L6 which is positioned between the oscillator inductances L5 and L7, and a ground or counterpoise 7 connection with the other end of the coil L6. The aerial is tuned for-transmitting by means of a variable condenser C4 also in the antenna circuit.

The operation of the system for receiving has been described in connection with the receiving circuitsof the system and for transmitting, above. It will be noted that the oscillator circuits are tuned to a required frequency which serves a dual function, being effective to produce the carrier wave in the transmitting antenna circuit Ta and cooperating with the frequency of the incoming signal as tuned in by the detector circuits D to produce a heterodyned frequency to pass through the intermediate frequency circuits Ar for receiving.

With the set properly adjusted transmitting and receiving at the same period of time has been accomplished. In order that the audio-frequency variations of the oscillator output will not be transmitted to the intermediate frequency amplifier along with the audio-frequency variations due to the incoming signal, the adjustable condenser C6 used to tune the first intermediatek amplifier T, as hereinbefore referred to, is also used as a bypass for such oscillator variations as may be present in that part' of the circuit. Further, it will be noted that the first input tube, VTl, `is used as a modulator at radio frequency, rather than the usual form of detector; this is due to the fact that the usual grid leak resistance and condenser are omitted and thereby the amplifying action of this tube tends to make the receiver part ofthe set more sensitive. This manner in which the first tube VT1, is used is probably the reason why there is no interference on the receiver while transmitting or modulating the carrier frequency as it was found that when this tube was used as a detector with the customary grid leak and condenser there was quite a lot of feed back'to the first part ofthe instrument,l causing disturbancein the second detector output. This was overcome by omitting the grid leak resistance and condenser from'thisfirst tube circuit and therefore. the first or input tube VTlis not used as! a detectortube, but as' a modulator at radio frequency, and no part of this circuit is sensitive to audio-frequency variation. f

`Referring to Figure 1, an application of the two-way signaling system between two stations is illustrated. It will be noted that each station' is equipped with twofaerials, one fortransmitting and one for receiving. Station No. 1 istuned to receive on 100 meters wave length and. to transmit on 103 meters and stationNo. '2 receives on 103 meters'and transmits on 100 meters, thatis 100 and 103 correspond to the respective wave lengths of the oscillating circuits of the two stations and their receiving wave lengths differ by vthree meters corresponding to the frequency of approximately eighty-seven kilocycles at said wave length range, namely, 100 and 103 vmetersto which the tuned intermediate or heterodyned frequency amplifierv circuits of the systems are adjusted to respond.

`Referring to Figure 3, a simplified form of i the system in accordance with this invention is diagrammatically shown. With but a few exceptions the detector, oscillator and modulator circuits are the same as those shown in Figures 2 and 2A, the same characters of reference being used to denote the similar parts. In the oscillator circuits, it will be noted that the variable condenser C2 has been arranged to bridge the grid coil L5 of the oscillator inductances as mentioned hereinbefore, and the plate tuning condenser C3 has been omitte'd.-y Otherwise, these circuits are the same. In this case, the heterodyned frequency is fed into a tuned intermediate frequency amplifier consisting of primary and secondary coupled inductances L10 and L11 respectively which is provided with a primary semi-variable or adjustable condenser C6 for tuning it. The intermediate frequency amplifier feeds into the second detector tube VI`5 to which the receiver R is connected. l

Referring to Figure 4, the circuit arrangements are substantially the same as that represented iu Figure 3 with the exception that a double grid tube. VT? is used in place ofboth the oscillator tube VT2 and transmitting modulator tube V'I3.V In this arrangement the oscillator grid inductance coil L5 is connected lwith one grid H2 of this tube and the modulating transformer Mod-T is connected with the other grid II1 thereof. Using a four elementtubein accordance with this arrangement has advantages over corresponding systems employing three element vtubes Vin that thesystem can be put up in a more compact set,'eliminates the necessity Vfor la number of eXtra parts and connections and reduces the current consumption to some eX- tent.

The operation of systems disclosed in Figures 3 and 4 is the same as that of the system shown in Figures 2 and 2A. These systems have been simplified but still maintain the same principles of the invention. l

The novel features which are believed t be inherent in the invention are defined in the appended claims.

I.claim:- 1. In a two-way radio signaling system, the combination with a receiver including detector, oscillator and intermediate or heterodyned frequency amplifier circuits, of a transmitter for operating simultaneously therewith including separatemodulating and antenna circuits coupled by the oscillator circuit of the receiver, and a filter between the modulating circuit and oscillator circuitoperative to prevent the passage of radiofrequency currents from the oscillator circuit.

2. In a two-way radio signaling system, thev combination of receiving antenna and detector circuits, an oscillating circuit cooperating therewith, an intermediate frequency circuit responsive t'o a heter-odyned frequency between the frequencies of the detector and oscillator circuitsfor receiving incoming signals, means for simultaneously modulating the current in the oscillator circuit by an audio frequency, said oscillating circuit including a single two grid oscillator tube of which one of the tube grids functions in the oscillator circuit in the production of high frequency oscillations for both receiving and transmitting and the other grid is connected with the transmitting audio frequency modulating means, and a radiating circuit coupled with said tube for transmitting oscillations of said oscillator as modulated by the audio frequency.

Y 3. In a two-way radio signaling system, the combination of a receiver and transmitter including a two grid oscillator tube, one grid of which tube functions in the production of continuous high frequency oscillations for both the receiver and transmitter to provide a common oscillator, the other grid of said oscillator tube being included in the transmitting circuit and operative to modulate the high frequency oscillations in accordance with the impressed audio frequencyV for transmitting outgoing signals.

4. .In a two-way radio signaling system, including a receiver and intercoupled transmitter for receiving and transmitting on separate wave lengths simultaneously, said receiver consisting of a receiving antenna circuit tunedl to one frequency, an oscillator tuned to a different frequency, and amplifying and detecting circuits including an intermediate frequency lamplifier tuned to respond tothe heterodyned frequency between the frequency ofthe receiving antenna circuit andfrequency of the oscillator, and said transmitter including a modulator connected with said oscillator of the receiver, and a radiatingpcircuit inductively coupled with said oscillator for transmitting at the frequency of the oscillator. l

y5. In a two-way radio signaling system, the combination with a receiver including, a receiving antenna circuit, an oscillator cooperating therewith, and an intermediate tuned frequency circuit responding to the differences in frequency between the receiving antenna circuit and said oscillator, and a receiving detector connected with the last said circuit, of a transmitter including a modulating circuit connected with said oscillator, and a separate transmitting antenna coupled with said oscillator.

6. In a combined radio signal receiving and transmitting apparatus, an antennafor receiving an incoming signal including a tuned circuity connected therewith, means for heterodyning said incoming signal including an oscillator which oscillates at a different frequency from that of the incoming signals, an intermediate circuit, a detector and a receiver connected therewith, a transmitting radiating circuit coupled to the oscillator, means for modulating the oscillations of said oscillator for transmitting signals at the frequency of said oscillator, and a filter or a bypass connected between the transmitting and receiving circuits to prevent interference between the transmitter and receiver and for tuning said intermediate circuit to the frequency difference between the frequency of the incoming signal and the frequency of the oscillator. Y

f 7. In a two-way radio signaling system, the combination with a receiver including an oscillating circuit with its oscillating tube, a transmitting modulator coupled therewith including a modulating tube, a source for supplying current tothe plates of both the oscillating and Vmodulating tubes, means to prevent audio variations in the current supplied to the plates of the two tubes, and means to prevent radio frequency currents from passing between the plates of the two tubes, of a filter or by-pass connected with the receiving circuits -operatingto by-pass variations in amplitude of the oscillator due to the modulator and prevent such variations from being detectedl in the receiving circuits, thereby preventing the transmitter from interfering with the receiver, whereby the interconnected transmitter and receiver may function independently and simultaneously.

In testimony whereof I hereunto afiiX my signature. o

LARRY L. SMITH. 

